A considerable fraction of carbon in the interstellar medium -20% or more -is in the form of polycyclic aromatic hydrocarbons (PAHs), and their mid infrared emission lines are dominated by bands related to this class of molecules (Joblin et al., 1992). When a PAH incorporates one or more atoms of nitrogen, that substitute the carbon atoms, it becomes a polycyclic aromatic nitrogen heterocycle (PANH). They can provide the missing link between the abundant PAHs chemistry at the ISM and the

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... ISM and the nucleobases that compose all living beings. Analyses of the PAHs features profiles, especially the 6.2µm feature, could indicate the presence of nitrogen incorporated to the rings. Peeters et al. (2002) has suggested the division of PAH spectra into three classes -A, B and C -depending on the variation's interpretation of the profile peak positions. Identification of the feature class can show if PANHs are present and how important they are for this emission. For this work, 206 galaxies (starburst-dominated, in general), extracted from the Spitzer/IRS ATLAS project (Hernán-Caballero e Hatziminaoglou, 2011), have their 6.2µm profiles fitted and distributed into the Peeter's classes. A total of 124 (60%) galaxies were classified as class A, 42 (20%) galaxies as class B and 3 (1.5%) galaxies as class C. The class A, corresponding to a central wavelength near 6.22µm, has only been explained by carbon replaced by nitrogen, despite other attempts of explanation (Hudgins et al., 2005). Besides, class B can represent a mix between PAHs and PANHs. Therefore, these spectra suggest a significant presence of PANHs, that could indicate another reservoir of nitrogen in the Universe, with density and temperature conditions different from those of gas phase and ices.